Internal combustion engines, including diesel engines, gasoline engines, natural gas engines, and other engines known in the art, exhaust a complex mixture of air pollutants. Among other things, the air pollutants are composed of solid particulates. Due to increased attention on the environment, exhaust emission standards have become more stringent and the amount of particulates emitted from an engine may be regulated depending on the type of engine, size of engine, and/or class of engine. These particulates can be very small and, for that reason, have historically been collected with a fine mesh ceramic or metallic filtration medium. Although effective at removing particulates, the fine mesh filtration mediums restrict the flow of exhaust and create an unacceptable level of back pressure within the engine when saturated with particulates.
An alternative method of collecting particulates from the exhaust flow of an engine is described in U.S. Pat. No. 5,458,850 (the '850 patent) issued to Krutzsch et al. on Oct. 17, 1995. The '850 patent discloses a method of reducing particulates in exhaust gases of an internal combustion engine. The method includes passing the exhaust through an electrostatic filter. As the exhaust passes through the electrostatic filter, a high voltage is applied between a central electrode and an outer electrode, thereby generating a high voltage field through which the exhaust passes. At the same time, small particulates mass together to form larger particulates (agglomeration). The strength and extent of the high voltage field are sized such that the particulates have a greater mass and size when leaving the electrostatic filter. The exhaust gases now having the larger particulates are directed into a particulate separator, which is in the form of a cyclone. The cyclone separator divides the exhaust flow into a particulate-free exhaust gas stream and a particulate-concentrated exhaust gas stream. The particulate-free exhaust gas stream is discharged to the atmosphere, while the particulate-concentrated exhaust gas stream is fed to a cavity resonator, in which it is exposed to an electromagnet field generated by a microwave source. At the same time microwave energy is applied to the particulate-concentrated exhaust gas stream, the particulates are heated to a temperature of combustion and burned away. The exhaust gas stream from which the particulates have been extensively removed are fed from the resonator to the atmosphere. In this manner, even small particulates may be removed from an exhaust stream, without causing a significant back pressure within the internal combustion engine.
Although perhaps effective at removing small particulates from an engine's exhaust flow without adversely affecting performance of the engine, the method of the '850 patent may be inefficient and complex. In particular, the voltage levels required to agglomerate the particulates may require significant energy from the engine, which may increase operational costs of the engine. And, the components required to agglomerate the particulates are numerous, expensive, and require complicated control strategies.
The disclosed exhaust system is directed to overcoming one or more of the problems set forth above.